Twitter warns that Firefox was caching private data – update

Twitter warns that users running the service in Firefox may have private data in the browser’s cache. Firefox caches data for seven days.

Twitter reports “recently discovered” that the way Mozilla Firefox caches data from Twitter may lead to the inadvertent storage of non-public data. In this way, private data such as information from direct messages can be exposed, for example if a Twitter user has logged into a system with Firefox from a third party. There are also malware tools that can search the cache of browsers.

The service has made changes to prevent personal data from ending up in the cache of Mozilla’s browser. Anyway, Firefox’s cache retention time is seven days, so data is deleted after that period. Chrome, Safari and other browsers didn’t have this problem, according to Twitter.

Firefox users can manually clear their cache through Options, Privacy & Security, Cookies and Website Data, and then clear the Cached Web Content data.

Update, Wednesday 8 April: The reason some browsers don’t cache direct messages from Twitter is that Twitter uses the Pragma: no-cache header in responses, Mozilla writes after an analysis. Pragma: no-cache is according to Mozilla non-standard and equal to Cache-Control: no-cache of http/1.1. The Pragma variant should only be used for backwards compatibility with http/1.0.